Compared with a conventional bulb, the light emitting diode (LED) has outstanding advantages, such as compact, long-life, low driving voltage/current, cracking resistance, no obvious thermal problem when lighting, mercury free (no pollution problem), high lighting efficiency (power saving), etc. In addition, the lighting efficiency of LEDs has been continuously improved in recent years. Hence, LEDs have gradually replaced fluorescent lamps and incandescent lamps in some fields, such as the scanner light source, the back or front light source of the liquid crystal display, the illumination for the instrument panel of automobile, the traffic signal lamps and the general lighting devices.
FIG. 1 is a cross sectional view showing a conventional light emitting diode. Referring to FIG. 1, a light emitting diode 100 mainly consists of a substrate 110, a N-type semiconductor layer 120, an electrode 130, a light emitting layer 140, a P-type semiconductor layer 150, a current-blocking layer 160, an electrode 170 and a current spreading layer 180. The N-type semiconductor layer 120, the light emitting layer 140, the P-type semiconductor layer 150, the current spreading layer 180, and the electrode 170 are sequentially formed on the substrate 110. In the conventional technique, to prevent light emitted by the portion of the light emitting layer 140 corresponding to the electrode 170 from being adsorbed or reflected by the electrode 170, a current-blocking layer 160 made of insulation material is formed between the P-type semiconductor layer 150 and the current spreading layer 180 and opposite to the electrode 170. In addition, the light emitting layer 140 only covers a portion of the N-type semiconductor layer 120, and the electrode 130 is disposed on a portion of the N-type semiconductor layer 120 that is not covered by the light emitting layer 140.
Referring also to FIG. 1, when an external circuit provides a voltage to the electrode 130 and the electrode 170, the current spreading layer 180 spreads a current C to two sides of the current-blocking layer 160 and conducts the current into the P-type semiconductor layer 150 such that the P-type semiconductor layer 150 provides electric holes to the light emitting layer 140. The electric holes and the electrons provided by the N-type semiconductor layer 120 are combined so as to emit the light. Simultaneously, because there is no current conducted into the portion of the P-type semiconductor layer 150 that is covered by the current-blocking layer 160, the portion of the P-type semiconductor layer 150 covered by the current-blocking layer 160 cannot provide electric holes to the light emitting layer 140. Accordingly, the portion of the light emitting layer 140 corresponding to the current-blocking layer 160 doesn't emit light.
As described above, the conventional light emitting diode 100 utilizes the current-blocking layer 160 to prevent the current under the electrode 170 from being conducted into the P-type semiconductor layer 150. As a result, the light can be emitted from the portion of the P-type semiconductor layer 150 which is not covered by the electrode 170. Accordingly, the light extraction efficiency of the light emitting diode 100 is improved. However, the current-blocking layer 160 consisting of the insulation material easily increases the electrical resistance between the current spreading layer 180 and the P-type semiconductor layer 150 and increases the forward voltage of the light emitting diode 100, so a life time of the light emitting diode 100 is decreased.
In addition, the binding force between the current spreading layer 180 and the P-type semiconductor layer 150 are also decreased because the step coverage between the current spreading layer 180 and the current-blocking layer 160. As a result, the light emitting diode 100 is easily damaged in the following wire bonding process due to having poor structure strength.